A packaged focal plane array comprises a detector array, an associated reference detector array and read-out circuit, and a transmissive cover that seals the detector array, reference detector array and read-out circuit. The cover may be sealed via a seal ring. The seal ring may comprise two components, a first component on the transmissive cover and a second component on the substrate with the detector array, reference detector array, and read-out circuit. The two components may be aligned and soldered together to seal the two components together.
In some scenarios, one of the surfaces of the transmissive cover may include an infrared shield that is typically made of the same metal (e.g., gold) used to form the two components of the seal rings. Accordingly, the solder used to seal the infrared detector wets to the shield just as it does the seal rings. If the solder migrates out from the seal rings and wets to the shield, the shield may draw more solder onto the shield. This could deplete the solder from the seal, preventing a hermetic seal, and could potentially short-circuit the reference detector array. One common way of preventing the solder from wetting to the shield is to make the dimensions of each shield only slightly larger than the dimensions of the corresponding reference detector array. The seal ring is then designed large enough so that there is a sufficient gap between the seal ring and the shield to prevent solder extruded during bonding process from wetting to the shield.